The effect of various wavelengths of light has been studied for the relative effectiveness in killing leukemic L1210 cancer cells incubated with hematoporphyrin. Investigations were performed on the enhancement of the photo-induced killing of L1210 after pre-incubation of the cells containig succinyl acetone which is known to argument the uptake of heme and hematoporphryin by cells. Increasing serum concentration in the medium was found to have protective effect on growth inhibition.